Levitation beds

ABSTRACT

The invention relates to a control system for a levitation bed in which the patient is supported on an air cushion composed of a plurality of air pockets forming a mattress and comprises an air duct for supplying air to the pockets, the flow of air being controlled by a damper or butterfly valve operated by an hydraulic cylinder energised by air from a static pressure transmitter which senses any change in pressure in the duct.

United States Patent [1 1 Howorth Oct. 21, 1975 LEVITATION BEDS [75] Inventor: Frederick Hugh Howorth, Chorley,

England Howorth Air Conditioning Limited, Lancaster, England 22 Filed: Mar. 25, 1974 21 Appl. No; 454,286

[73] Assignee:

[30] Foreign Application Priority Data Apr, 19, 1973 United Kingdom l9l3l/73 [52] US. Cl. 5/348 R; 297/57 [51] Int. Cl. A47C 27/08 [58] Field of Search 5/347, 348-350;

[56] References Cited UNITED STATES PATENTS 3,340,55] 9/1967 Hopkins 5/348 R 3,822,425 7/1974 Scales 5/348 R Primary Examiner-Paul R. Gilliam Assistant Examiher-Andrew M. Calvert Attorney, Agent, or FirmNorris and Bateman [57] ABSTRACT 6 Claims, 5 Drawing Figures US. Patent Oct. 21, 1975 Sheet 1 of3 3,913,156

US. Patent Oct.21,1975 Sheet2of3 3,913,156

US. Patent Oct.21, 1975 Sheet30f3 3,913,156

lllllll ul /l III. II ll'llllllllll suffering from severeburns. Earlier beds 'of.- this construction have been found to operate-satisfactorily only as long as the patient does not move. v

This earlier bed is an inflatable chambenwith-an outlet formed bya number of pockets which :is self-- adjusting .inithree plane'srAs eachzpocket inflates it is forcedagainstits neighbour and it alsomeetsthe oppo-. site pockets along: the mid-line of the bed and along-the mid-line of each leg. After the patient is put'on the inr flated bedthepressure is adjusted so that-the pockets are sdepressed sufficiently by the downward thrust of the body to allow pressurised air toleak between the body and the toptsurface of the pockets, Those portions of the pockets beneath the body are subject tothe same pressures on their inner and'outer surfaces and thus fall.

away from-the patientwhilethoseportions outside the body profile remain inflated...=-

According tothe invention, a control system for an air support levitation bedto maintain a. substantially constant air pressure in the pockets thereof forming .a mattress-comprises anair duct for supplying air to the pockets a.damper ,or valve in. the duct to open and.reg-. ulate .the supplyof. air, so that the. air maybe regulated tooppose the weight; of various patientssuch as chil-,

drenand .adults, and;means once this equilibrium has been established ,to maintain, the equilibrium, automati cally, even when .the air leak is varieddue to the patient moving about; a,pres sure tapping or sensor todetect any variation in, air pressure in the pockets; a pneur. matic, electric or electro-pneumatic pressure regulat; ing and compensating system, calibrated to the weights of patients, controlling the supply of compressed air to a pneumatic cylinder, the piston of which operates a linkage to hold the damper or valve in the required position to obtain the correct constant air pressure to sup port the weight of the patient, and to open the damper or valve when any drop in pressure occurs in the pockets of the bed due to the movement of the patient, and to return to the required holding pressure once movement of the patient has stopped.

The invention will be described with reference to the accompanying drawings:

FIG. 1 is an end elevation of a bed.

FlG. 2 is a part side elevation of same showing diagrammatically a control circuit therefor.

FIG. 3 is a similar view of a further circuit arrangement.

FIG. 4 is a similar view incorporating a safety circuit.

A levitation air bed A is formed with a plurality of open ended pockets a forming a mattress extending from both sides of the bed frame to meet on the longitudinal centre line of the bed. Air is supplied from a duct A to an annular chamber formed as an envelope a surrounding the pockets a. The air passes into the pockets a the outer ends of which are connected to the envelope. The air inflates the pockets a on each side of the bed and as each pocket is inflated it is forced against its neighbour and also meets the opposite pocket along the central longitudinal axis of the bed.

A control of the air supply is provided to compensate for excessive escape of air from the pockets and the subsequent loss of levitation pressure when the movement of a patient on the bed upsets the equilibrium of airpressure in the pockets.

The air supply to-the duct A' under a pressure of be tween 6 inches and 15 inches water gauge, is controlled by a damper or butterfly valve 1 actuated by a piston in a pneumatic cylinder 2 through alinkage 3. Compressedair at a reference pressure of 20 p.s.i. is fed direct to a receiver 4 and also indirectly to the receiver through a restrictor valve 6 and a gradual switch. Compressed air from the restrictor valve 6 is connected to a differential static" pressure transmitter 5 which senses the change in air pressure in the duct througha small bo're 'pipeTconnectedto a static tapping 8. The air support or levitation bed is supplied with sterile condi- "tioned air froma remote air feed system. The air pressure at the 'bed is adjusted according to the "weight of v the patient. The correct air pressure for the weight of the' patientis selected by a variable control valve 9 which; allows the transmitter 5 to leak-off compressed airlfromitherestrictor valve 6 which in turn, reduces the compressed air feedback to the receiver. The receiver 4 automatically adjusts the correct compressed air pressure to feed the cylinder 2 andthis moves the damper 1 to the correct position to maintain a constant air' pressure at the bed. Any drop in air pressure at the bed, due to the movement of the patient, will immediately be sensed by the static air pressure tapping 7 and conveyed to the transmitter 5 which leaks off more compressed air from the restric tor valve 6 which then reduces the compressed air pressure feed back to the receiver 4. The receiver 4 automatically reduces the compressed 'air feed to the cylinder 2 which in turn opensjtlie -damper 1 and allows more air tothe bed,

thus restoring the required levitating pressure.

In an alternative arrangement F IG. 3 a variable control feeds compressed air at a :maximum pressure of 20 p.s.i. through s solenoid valve 10 to the cylinder 2. A single phase electrical supply is connected to terminals which in turn feed the solenoid valve 10. The neutral line is connected direct to the solenoid valve 10 and the line supply passes through a normally closed microswitch 11 inside an air pressure switch 12 before being connected to the normally closed solenoid valve. The air pressure switch 12 is connected by a small bore pipe 13 to the static pressure tapping 8. A fall in pressure in the supply duct A is sensed. by the pressure switch through the tapping 8 which opens the micro-switch 11 to cut off the electrical supply to the solenoid valve 10 and opens the valve. This sequence allows compressed air to escape from the cylinder 2 which opens the damper 1 or valve.

The air support system of the bed is supplied with sterile conditioned air from a remote air plant. The air pressure at the bed is adjusted according to the weight of the patient and may vary from 6 inches to 15 inches water gauge. The correct air pressure for the patients weight is selected with the variable control which allows the correct pressure of compressed air to be fed to the cylinder 2 which in turn, adjusts the damper l to the correct levitating position. The compensating air pressure switch 12 is pre-set to operate at an air pressure below the normal operating range required for levitating the patient. If the patient moves excessively, when in a state of levitation, then this allows more air to escape past the patient and hence the pressure in the bed is lowered and the patient begins to sink into the bed until the pressure in the bed reaches the fixed setting of the air pressure switch. This immediately breaks.

the micro-switch ll inside the pressure switch and opens the solenoid l releasing the compressed air in the cylinder 2 which in turn, opens the damper l to admit full air to the bed. This gives maximum pressure in the bed and automatically raises the patient to the original setting of the variable control. The pressure switch 12 will close the micro-switch 11 as the pressure in the bed increases past the fixed setting thus reestablishing a state of equilibrium.

In the arrangement shown in FIG. 4 a safety feature is incorporated to prevent the patient from falling to the bottom of the bed if the pneumatic compensating mechanism acts too slowly to withstand a sudden violent movement.

An electric pressure switch 15 and a solenoid valve 16 are provided, the pressure switch having an adjustable range and is set at a pressure below that required to levitate the patient. If the patient reacts violently and the pneumatic system does not compensate in time, then the electric pressure switch 15 immediately detects the drop in pressure and immediately energises the solenoid valve 10, which in turn, evacuates the damper control cylinder 2 and allows full air volume onto the bed. This reaction lifts the patient to the top of the bed and allows the pneumatic system to take over the nonnal levitating pressure control function.

What we claim is:

1. In combination, a levitation bed of the type having a pressurized chamber the outlet of which is formed by a plurality of inflatable pockets arranged as a mattress for underlying a patient, means for supplying air under pressure to said chamber and pockets whereby the weight of a patient on the bed may cause escape of pressurized air to establish and maintain in equilibrium a supporting air cushion between the upper surfaces of the pockets and the body of the patient, means including valve means for controlling said supply air pressure,

and means responsive to a change of equilibrium air pressure at said cushion due for example to movement of the patient relative to the pockets for automatically compensatively varying the air pressure derived from said supply for maintaining substantially constant equilibrium air pressure at said cushion and preventing the sensing means are correlated and having an output connected to control said valve means.

4. The combination defined in claim 1,,wherein said valve means comprises a valve element movablein a supply duct and connected to be operated by a fluid pressure motor, and means is provided for sensing the pressure in said supply duct downstream of said element, correlating it with a reference pressure and applying a resultant control pressure to said motor.

5. In the combination defined in claim 4, means for varying the reference pressure to vary said supply pressure for establishing equilibriumin said air cushion.

6. In the combination defined in claim 4, a solenoid valve in the line for applyingsaid resultant pressure to w said motor and an energizing circuit for said solenoid 5 valve containing a normally open pressure switch that closes in response to a decrease in said supply pressure sensed by said sensing means to dire'ctly operate said motor to open said valve means in the event of delayed action of said means correlating the reference and sensed supply pressures. Y 

1. In combination, a levitation bed of the type having a pressurized chamber the outlet of which is formed by a plurality of inflatable pockets arranged as a mattress for underlying a patient, means for supplying air under pressure to said chamber and pockets whereby the weight of a patient on the bed may cause escape of pressurized air to establish and maintain in equilibrium a supporting air cushion between the upper surfaces of the pockets and the body of the patient, means including valve means for controlling said supply air pressure, and means responsive to a change of equilibrium air pressure at said cushion due for example to movement of the patient relative to the pockets for automatically compensatively varying the air pressure derived from said supply for maintaining substantially constant equilibrium air pressure at said cushion and preventing the patient''s body from dropping into contact with said pockets.
 2. In the combination defined in claim 1, said means for varying the supply air pressure comprising means for sensing a change in air pressure downstream of said valve means operatively connected to said valve means.
 3. In the combination defined in claim 2, means providing a reference pressure, and means wherein said reference pressure and the pressure derived from said sensing means are correlated and having an output connected to control said valve means.
 4. The combination defined in claim 1, wherein said valve means comprises a valve element movable in a supply duct and connected to be operated by a fluid pressure motor, and means is provided for sensing the pressure in said supply duct downstream of said element, correlating it with a reference pressure and applying a resultant control pressure to said motor.
 5. In the combination defined in claim 4, means for varying the reference pressure to vary said supply pressure for establishing equilibrium in said air cushion.
 6. In the combination defined in claim 4, a solenoid valve in the line for applying said resultant pressure to said motor and an energizing circuit for said solenoid valve containing a normally open pressure switch that closes in response to a decrease in said supply pressure sensed by said sensing means to directly operate said motor to open said valve means in the event of delayed action of said means correlating the reference and sensed supply pressures. 